Control system for aerial photography



Jan. 10, 1961 s. P. wlLLlTs ET AL 2,967,470

CONTROL SYSTEM ROR AERIAL PHOTOGRAPHY Filed March 28, 1957 8 Sheets-Sheet 1 Mimi A7' RNEK Jan. 10, 1961 s. P.w1| |Ts ET AL 2,967,470

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Filed March 2s, 1957 A s sheets-sheet 2 MANUAL COMPUTER /84 ,o ,y r Il' a 0 a5 a 1| l 8 "MII OPTICAL SCANNER a2 (85 7 35 SCANNER CONVERTER E' SCANNER; Q1 f MANUAL CENTRAL COMPUTER ,faQ/27 if@ STATION *T2-9 COMPUTER j' +D.C.

UNO POTENTIOMETER SGNAL GRO DHL y |u|||||||||||| VELOCITY SCALE |||||u|| Hl-ALT. ER OR |oER A TTORNEK Jan. 10, 1961 s. P. wlLLlTs ET AL 2,967,470

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Filed March 28. 1957 8 Sheets-Sheet 3 27 Hl-ALT.

NI/ENTORS W 474 Q' n/z Y @yMmm-C ATTORNEA/ Jan. 10, 1961 s. P. wlLLlTs ETAL 2,967,470 Y CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Filed March 2s. 1957 s sheetssheet 4 SYNCHRO TRANSMITTER Jan. 1o, 1961 s. P. wlLLlTs ETAL 2,967,470

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Filed March 28. 1957 8 Sheets-Sheet 5 I r t ,14 zal /NVENTORS- +I" uNDERsPEEo-t M MM5. mm 0` g1( m, mm? l.

3W 2- 02 A W LovERsPEED ATTORNEK Jan. 10, 1961 s. P. wlLLlTs ETAL 2,967,470

CONTROL SYSTEM FOR AERAL PHOTOGRAPHY Filed March 28, 1957 8 Sheets-Sheet 6 3&1

/N VEN TORS ATTORNEK Jan- 10, 1961 s. P. wlLLlTs ET A1. 2,967,470

CONTROL SYSTEM FOR AERIAL PHOTOGRAPHY Filed March 28, 1957 8 Sheets-Sheet 7 OTHER SOLENOIDS Jan. 1o, 1961 S. P. WlLLlTS ETAI.

CONTROL. SYSTEM FOR AERIAL PHOTOGRAPHY Filed March 28, 1957 8 Sheets-Sheet 8 ff f7, 4/0 5.9/ j '38 409 37.9 .371

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4%/ f :L x 441/ 442/" 'l'. d'="+" By //f T Arrow/v5).

ie Sra l Chicago Aerial Industries, Inc., Melrose Park, lll.,

a corporation of Delaware Filed Mar. 2s, 1957, ser. No. 649,018 32 Claims. (Cl. 95-'12.5)

This invention relates generally to a control system for aerial cameras and more particularly to a new and improved control system for one or more aerial cameras in which the picture taking rate and motion imparted to film or camera is controlled to compensate for image motion at the photographic plane.

One of the basic requirements of an aerial camera control system is that it produce negatives of high resolution. One of the features which reduces photographic resolution is image motion. It is known that the effect of image motion may be offset by supplying a cornpensatory motion to vthe film or to the camera during exposure. h

In View of the increasing capability for speed in present day aircraft, the need for more accurate means to decrease the blurring effect produced by the relative object motion during photographic exposure has become more significant. In the prior art, this compensation has usually been made b y rotating the aerial camera at a rate such that the camera optical axes remain aligned with a fixed point on the objectI plane during exposure or, alternatively, by moving the film in the camera at a rate such that a point on the iilm remains aligned with a fixed point on lthe object plane during exposure.

These techniques, which frequently are referred to as image motion compensation or IMC, generally have proven satisfactory since it has been found that the change of the distance or angular position usually is of secondary importance. l Such compensatory motion may be defined by the following equation.

:1.689FZ sine 6 where v=required image motion compensating velocity in inches per second. F=camera focal length in inches. Y V=true aircraft velocity relative to ground in knots. H-=aircraft altitude (terrain clearance) in feet.

:camera focal axis depression angle below the horizontal in degrees.

It also is frequently required that an aerial photographic system be capable of taking pictures at discrete periodic intervals. It may further be necessary that sequential frames or pictures have a predetermined amount of overlap. This overlap, usually expressed as a percentage, is useful in providing stereoscopic viewing of the resultant prints and also in mapping for the purpose of keying a series of photographs together. For maximum usefulness lthe overlap must be maintained with good precision to avoid ,changing the trigonometric rela tionships used in preparing a topographic map. By way of example, the accuracy required by the military services varies between plus or minus 5% and plus or minus 3%. As reduced to practice in the present invention, these limits are substantially bettered.

aii@ Patented Jan. l0, 1961 It will readily be understood by those skilled in the art that the overlapV of successive exposures is dependent on the time interval between exposures or the rate at which exposures are made per unit of time. An equation which may be used to determine the picture taking rate for any value of overlap from 0 to 100% is:

m-K snm@ 0 where For the purpose of the description which follows it should be noted that in Equations l and 2 above, velocity (V) and altitude (H) of the aircraft are the only variables subject to change during flight. These elements are designated as in-flight variables. The remaining elements of Equations 1V and 2 are known before the flight and hence are designated as pre-flight variables.

Several control systems for aerial photography which provide for the control of the picture taking rate and image motion compensation are known but the degree of accuracy attained by such prior art systems has not proved entirely satisfactory. For the control of IMC, the majority of prior art systems have means for providing an electrical potential proportional to aircraft velocity and altitude. This potential then is fed into an electronic computer in combination with the data corresponding to the pre-Hight variables to provide an output voltage proportional to all of the variables. This output voltage then is applied to a conventional velocity servo mechanism to control the speed of the film drive motor or the velocity of a camera mount.

The accuracy of systems of the type just described is dependent upon a number of independent variables. These include the accuracy with which the velocity to altitude ratio V/H is determined and maintained, the degree of precision with which this ratio is converted to an electrical potential, the accuracy of the electronic computer that integrates the pre-night Variables into the computationand finally, the ability of the velocity servo mechanism to translate the computed output potential into the desired velocity.

Further, a variety of systems have hitherto been devised to control the picture taking interval. One of the most common of these is a manually set timing device which uses a constant speed drive mechanism to control a switch initiated camera operation. Devices of this type normally are referred to as intervalometers an although they generally are accurate, they also are cumbersorne to utilize since they require laborious calculations on the part of the operator. They also have the disadvantage that when either of the in-flight variables is changed, the calculations must be repeated and reentered into the intervalometer. This obviously is unsatisfactory under conditions such as military reconnaissance Where evasive action often must be taken during a photographic run.

lt has not hitherto been knownhow to devise an aerial photographic control system which is capable of providing image motion compensation and control of the pic' ture taking rate with the precision required for present day aircraft. More simply, prior to this invention there has not been available aerial camera control mechanisms having the accuracy required for reducing the factors detracting from photographic resolution to only the camera optical system, the film characteristics, and ight turbulence.

Accordingly, it is a primary object of this invention to provide a new control system for aerial photography which is characterized by its improved accuracy of image motion compensation and its control of the picture taking rate. y Y Y It is a more specific object of this invention to provide an improved aerial photographic control system capable of precisely measuring aircraft angular velocity and accurately converting this information into compensatory film veloci-ty and picture taking rate control.

It is still another object of this invention to provide such an improved aerial pho-tographic control system in which the entry and computation of pre-Hight variables is greatly simplified and which is capable of automatically adjusting to changes in the in-ight variables.

It is a further object of this invention to provide an improved control system for aerial photography which permits continuous monitoring of the source of information of in-flight data.

lt is still another object of this invention to provide such a control system having means for substantially eliminating any computation for the manual entry of the in-iiight data when it is not available from an automatically operating source.

Still another object of this invention is the provision of means for synchronizing the operation of a camera with a mechanical shaft rotation in a more precise manner than was heretofore possible.

It is another object of this invention to provide a control system for aerial photography adapted to control several different types of cameras without requiring modification of the cameras. More particularly, it is an object of this invention to provide an improved camera control system for image motion compensation and picture taking interval control which is not limited as to film format dimensions, film transport mechanism and camera focal length.

It is a still further object of this invention to provide an improved system capable of synchronizing the eX- -posures of a plurality of cameras which have their respective optical axes at various angles of depression relative Vto the horizontal.

Still another object of this invention is the provision of an improved aerial camera control system capable of operatingseveral cameras in a predetermined repetitive sequence.

Still another object of this invention is the provision of a system capable of selective action in accordance with the camera focal axis depression angle below the horizontal wherein image motion compensation and picture taking rate is readjusted to the correct value correspondlng to `this angle each time the angle is changed.

In accordance with a specific illustrative embodiment of the invention these and other objects are attained in a novel aerial camera control system which employs mechanical analogue principles whereby the aircraft angular velocity data V/H is converted to a D.C. potential and this potential then is translated into a corresponding mechanical shaft rotation. Calculations of the picture taking rate and IMC then are effected by a gear ratio changmg means to the end that integration of the pre-flight variables is accomplished with substantially zero error. This results in a substantial increase in accuracy over aerial photographic control systems now in use.

A feature of the invention is the use of a rotary synchronous transmitter driven in accordance with the shaft rotation to control the film velocity by means of aposiltional servo mechanism. Thus, in one aspect of this invention, precise control of film velocity is achieved by utilizing ak positional servo mechanism as a Velocity control device. This unique arrangement is very effective for even though a positional servo mechanism is subject to certain positional errors with respect to the rotary synchronous transmitter, its angular velocity error essentially is zero.

ln another feature of theinvention, the rotary synchronous transmitter drivenv by the shaft rotation in accordance with the angular velocity' data V/H is Vused to control the rocking motion of a swinging or ,IMC camera mount. Thus, the camera in the mount is rocked in an arc at an angular rate corresponding to the V/H data.

Accurate measurement of the aircraft angular velocity and the correction of errors which may result both in the determination of the aircraft angular velocity data. and the conversion of this datato compensating film velocity and picture taking interval control information is achieved through the use of an optical view finder which cooperates with a servo mechanism to the end that the compensatory film velocity and picture taking interval control information is present in the view finder field of view as moving grid lines. In accordance with this invention these moving grid lines move in synchronism with the terrain only when the determination and conversion of aircraft angular velocity is correct.

Still another feature of this invention is the provision of a variable speed transmission in combination with a servo mechanism, a rotary synchronous transmitter and cam operated switches to provide compensatory film velocity control and control of the picture taking interval for various cameras in accordance with camera focal length, film format size, focal axis and depression angle below the horizontal. One aspect of the invention is that the rotary synchronous transmitter and the cam operated switches are utilized to provide compensatory film velocity control and control of picture taking rate, respectively.

Still another feature of this invention is the provision of image motion compensation without restriction as to camera film transport mechanism, lens focal length, or lm format size by means of a positional servo mechanism which is adapted to cooperate with a pivotable mount and a mount actuating device to the end that the entire camera vassembly is rocked at a compensatory angular velocity.

During the course of an aerial photographic Hight, it frequently is necessary to obtain photographs at velocity to altitude ratios which exceed the limitations of a single camera as for example, where the picture taking interval becomes less than the camera recycle time, Such limitations are circumvented in accordance with a feature of this invention by a novel arrangement for operating a plurality of cameras in a predetermined repetitive sequence. This result is realized in one illustrative embodiment by the use of cam operated switches, in combination with a variable speed transmission and velocity servo mecha.

nism, as pulse rate dividers and distributors. These act to distribute the basic single camera exposure initiating pulses among two or more channels whose exposure initiating pulse rates then become times the basic rate where lN is the number of cameras to be operated in the repetitive sequence.

Still another feature of the invention is the synchroniza- Y tion, however, and its advantages reference is had to the accompanying drawings and descriptive matter in which adattato E is illiistfated sval spiiic iliustrative embodiments of the invention:

In the drawings: v

Figure 1 is a block diagram illustration afan aerial camera control system embodying features of this invention;

Figure 2 is a schematic and block diagram representation of the invention illustrating the manual computer or automatic scanner control of the central computer;

Figure 3 is a diagrammatic illustration showing in greater detail the construction of the manual computer;

Figures 4, 5, 6,;*7 and 8 illustrate the construction of the range gear changing mechanism; A

Figure 9 shows the construction of illustrative station computer; v v c Y I Figure 10 is a simplied schematic diagram illustrating the connection ofv two pulse cameras for either simultaneous or alternate sequential operation; Y

Figure 11 is asimpliiied schematic andblock diagram illustrating the connection of an` autocycle camera to the camera control system ofthe invention; A,

Figures 12, 13 and 14 are waveformdiagrams illustrating the operation ofthe circuits of Figures 11 and 1 5;

Figure 1'5 is a schematic diagram 'of a servo amplifier embodying the invention; Y

Figure 16 is a simplified schematic and block diagram illustrating the control system connections for the simultaneous operation of two pulse VIMC cameras;

"Figure 17 is a Simplilied schematic and block diagram showing a pulse IMC camera connected for day or night operation; Y y V Y Figures 18 and 19 illustrate the operation of a pulse camera in the IMC camera mount when connected with a camera control system in accordance with the invention;

Figure 20 illustrates the operation of the camera control system with a camera in a rotatable mount but not provided with an IMC mount actuator;V

Figure 21 is a schematic and block diagram of an alter'- nate station computer and pulse distribution system for pulse operated cameras;

Figure 22 illustrates/1a switch of the type which may be used with the station computer of the present invention;

Figure 23 shows in detail the construction of an embodiment of station computer which may be utilized in the system of Figure 2l;

Figure 24 is a simplified schematic of the electrical portion of the station computer shown in Figures 21 and 23; and

Figures 25, 26, 27 and 28 illustrate the principles of the View finder, as shown in Figure 2.

Referring now to the drawing and more particularly to Figure l, there is shown in block diagram form an' illustrative aerial camera control system whichisv representative of the general principles of the invention. The system comprises an optical scanner, designated b'y the reference numeral it), which advantageously may serve as one source of in-ight variable data, namely velocity, V, and altitude above the terrain H. Optical scanner 10 may take any suitable form and advantageously may be as shown in the patent to D. Hancock, Ir. and H. E. Meinema, 2,413,349, issued December 31, 1946. In operation, scanner 10 originates an electrical signal proportional to the Velocity to altitude ratio, hereinafter referred to as V/H. The scanner signal is applied to a scanner converter 11 where it is converted to a D.C. signal, designated as ER, having an amplitude proportional to the scanner signal. Advantageously, scanner converter 11 may be constructed as disclosed in the above-identidad Hancock and Meinema patent.

The D.C. voltage output ER of scanner converter 11 is applied to a manual computer 12 which also serves as a manually operable alternate source of V/H information in a manner further described below. A switch on manual computer 12 enables the operator to choose between the manual computet island 'the pticalspan#` ner i0 as the source of V/H infomation' forth 'camera control system. From manual computer `12, the D.C. signal ER is transmitted to a central computer designated generally at 14. f v c Central computer 1 4 comprises a velocity servo system 15, a gear changing mechanism 16, a linel shaft I7 coupled to the gear changing mechanism V16' and a synchro transmitter 18 together with a plurality of indi# vidual station computer units 19, 20, .21 and 22 each having a station computer 29 coupled to line shaft 17.

In accordance with a feature of this invention, the D.C. voltage ER is converted to a mechanical shaft rotation in the central computer 14. As will become apparent from the more detailed description given hereinbelow, calculations of the picture taking rate and IMC are made by unique gear ratio changing means to the eiid thatthe integration of the pre-fiight variables into the computation is accomplished with substantiallyl Zero error. This results in a substantial increase in accuracy over the prior art aerial photographic control systems heretofore utilized.

The conversion ofthe ER voltage to a shaft rotation is eiected in the velocity servo system 15 by the D.C. generator 23, the servo motor 24 and the amplifier 25 which responds to the ER voltage to vary the speed of motor 24 in accordance with the amplitude of the ER control signal. Motor 24 has its shaft coupled to the range gear changing mechanism 16 which transmits the motorcshaft velocity at a ratio of 1:1 or 1:1() in accordance with' a control signal received over conductor 27 from either the scanner converter 11 or the manual computer 12,

Coupled `to the output of the range gear changing mechanism 16 is a line shaft 17 which in turn is coupled to a synchro transmitter 18. The output of synchro transmitter 13, as applied over conductor 28k to the control system, is a rotational data reference signalV 4which is a function of V/H. A plurality of individual station computer units such as units 19, 20, 2 and 2Q2, .also are coupled to the line shaft 17, as by means of suitable bevel gears andthe like. l l l Each of the station computer units comprises a station computer 29 in the form of a gear changing unit which is adapted to provide a plurality of changeable gear ratios torpermit computation for desired overlap, focal length, format size and depression angle, otherwise known as the pre-'flight variables. The' rotational output of each station computer 29 serves to drive the rotor of a synchro transmitter 30 at a speedA corresponding to the computed camera cycling rate to thereby provide a rotational IMC reference Voltage for one or more cooperating cameras at a given carne'ra station. TheV output of each station computer 29 also drives pulse switching cam means 31 to provide one or more switch closures for pulsing a single camera or camera array, or two or more cameras' operating sequentially. Y 'Ihus, each station computer 29 is capable of supplying both IMC and pulse information to a camera station.

At ycamera station 1 in Figure l there are shown two pulse type cameras 32 and 33 connected for sequential operation. A pulse camera, as the name implies, operates on the basis of pulsed control signals. When aypulse is received by the camera it actuates the camera shatter which then initiates its own signal to command nlm winding and rewinding of the shutter if necessary. Als cameras lof this type operate with a single pulsecgiovernf ing the picture taking rate, it is necessary that the time separation of sequential pulses Ibe greater than lthe camera recycle time. When the pulseseplaration is less than' the camera recycle time it necessary` to use"l .e than one camera and to distribute the' control pulses between cameras. l l c i v In the two puls camera system shown *stationx l, the station computer output speed is decreased bysuitra` ble gearing to one-half of its normal speed and the two pulse switches are provided 180 apart. Each camera is connected to one switch, as for example, camera 32 to switch 34, and camera 33 to switch 35. In this manner each pulse to a camera occurs at the time it'would occur if there had been no gear reduction to the cam 31 operating the switches and each camera then is operated at one-half of the picture taking rate. It will be appreciated that a gear reduction to one-fourth speed for the cam and four switches would provide for sequential operation of four cameras, and, similarly, a gear reduction to one-third speed and three switches would pio vide for sequential operation of three cameras. Further, a single camera or single camera array may be operated from a station computer having two or more switches and having the switch operating cam appropriately reduced in speed merely by connecting all of the switches together, as illustrated at camera stations 3 and 4 in Figure 1.

Camera station 2 comprises an autocycle camera 36 with its associated servo amplifier 37. Autocycle cameras, or camera magazines, are controlled by an IMC command signal. This command -signal controls film speed in that the film holding platen and/or the film is moved at IMC speed and the camera or magazine originates a shutter tripping pulse while the film is moving at this speed. The film is then advanced, normally at a faster rate than IMC speed, to supply fresh film to the exposure area, after which IMC speed is resumed, the shutter tripped, and the cycle repeated. Cameras of this type provide an overlap of sequential exposure based only on camera design.

Similar to the autocycle cameras with reference only to the control signal required are strip cameras. The IMC command signal controls the speed of the film to synchronize it with the image of the ground as the film moves continuously past an open slit.

The illustrative autocycle camera 36 shown at camera station 2 in Figure l is adapted to be used in an azimuth mount 38 which corrects the alignment of the camera to compensate for aircraft drift. As illustrated, the autocycle camera 36 receives the IMC command signal from the synchro transmitter in station computer unit 21 through servo amplifier 37 and azimuth mount 38 receives the drift alignment signal from the viewfinder 50.

A tri-camera array comprising cameras 39, 40 and 4l, having similar parameters as described above, is shown at camera station 3 connected to be pulsed from the paralleled pulse switches at station computer unit 20. Manifestly, such an arrangement is desirable since the pre-Hight data is identical for cameras 39, 40 and 4l.

Camera station 4 in Figure 1 comprises a swinging or IMC mount 42 which supports a pulse camera 43. The IMC mount 42 together with its servo amplifier 44 achieves image motion compensation by rocking camera 43 in an arc at an angular rate corresponding to the velocity to altitude ratio V/H. As shown, the camera 43 receives its control pulses from the paralleled pulse switches in station computer unit 19, and the IMC mount 42 and servo amplifier 44 receive the V/H data from the synchro transmitter 18 in t'ne central computer.

While the four camera stations shown in Figure l illustrate four different camera configurations which advantageously may be used with the novel camera control system of the invention, it will be understood by those skilled in the art that advantageously numerous other camera configurations may be used therewith with equally successful results. For example, all of the camera stations could be provided with pulse IMC cameras for a night reconnaissance flight. In such an application the camera shutter is opened and the film is moved continuously in the camera at a speed determined by an IMC command signal. Pulses from a station computer release a flare cartridge or bomb at intervals in accordance with the desired picture taking rate. The explosion of the flare cartridge or bomb originates a second pulse.

from a flare detector which closes the shutter and causes the'lilm to recycle after which the shutter reopens. The next computer pulse repeats the sequence, etc. 1 Cameras of this type may be used sequentially in the same manner as pulse cameras. l

Day operation of pulse IMC cameras differs principally from night operation in that the computerr pulse operates a conventional shutter in place of releasing a flare cartridge or bomb. After shutter closure, the ilm is advanced and the lm velocity returns to the IMC rate until the next shutter operating control pulse. By this method it is possible to vary the overlap of sequential exposures as contrasted with autocycle cameras where this is not possible.-

The aerial camera control system shown in Figure 1 also comprises a plurality of station control units 45, 46, 47 and 48 which advantageously may include on-off switches for supplying power to camera stations l, 2, 3 and 4, respectively. In accordance with an aspect of this invention the supplying of power to the camera stations as well as to other system components, such as optical scanner 10, scanner converter 21, etc., does not permit the taking of pictures but merely permits warm-up of these various components. Picture taking commences when an operating switch, which may be located at any convenient place in the aircraft, is closed.

The camera control system shown in Figure l also includes a flare control 49 and a viewfinder shown generally at 50, which is described in greater detail below.

As explained heretofore there is more than one possible source for the V/H control data. A preferred arrangement for the camera control system of the invention would include both the optical scanner 10 together with the scanner converter Il and the manual computer 12, although it will be understood that only one such source is required.

The optical scanner 10 and its converter 11 function as an automatic source of V/H control data in accordance with the Hancock and Meinema patent identified above. Briefly, the optical scanner 10 originates an electrical signal which has a frequency proportional to the V/H ratio. The scanner converter 11 converts this frequency to a D.C. voltage ER which has an amplitude proportional to this frequency.

The alternative source of V/H information, the manual computer 12, is shown in greater detail in Figures 2 and 3 of the drawing. The manual computer 12 comprises a double pole, double throw switch 51 which includes a switch blade 52 operatively associated with a pair of stationary contacts 53 and 54, and a switch blade 55 ganged to switch blade 52 and operatively associated with a pair of stationary contacts 56 and 57. Stationary contacts 53 and 56 are connected to the output of scanner converter 11 and in the operating position of switch 5I shown in Figure 2 the ER control signal from the scanner converter is applied through switch blades 52 and to the central computer 14. Stationary contacts 54 and 57 of switch 51 are connected to terminals of switch 83 in the manual computer potentiometer 5S and in the other operating position of switch 5i, the ER control signal is applied from potentiometer 58 through switch blades 52l and 55 to central computer I4.

The manual computer potentiometer 58 is constructed to permit the shaft with the wiper and the housing to be rotated separately. This is better seen in Figure 3 in which a knob 59 on hollow shaft 6u is shown attached to a gear 61. Hollow shaft 60 is rotatably mounted on stud 62 and is restrained from axial motion b'y retainer 63. Advantageously, stud 62 may be secured to the support housing 64 in any suitable manner.

Gear 6I meshes with gear 65 which is iixed to the potentiometer shaft o16, Shaft 66 is rotatably mounted in bearings 67 and 68 which are fixed to the support housing 64. An altitude scaler69vis axed to gear 65 to the end that rotation of knob 59 also rotates potenasoma-o 9L tiometer shaf-t @Si to provide an indication of the magnitude of` rotation by means of the scale 69 and an in-Y dicator marie (not shown) attached to the support housing 64.

The velocit-y sca-1e 7G and the potentiometer housing '71 are actuated in a similar mannen. Knob 72 is attached Vto a hollow shaft 713 which in turn is attached to gear 74; Hollow shaft 7%V is rotatably mounted on stud 75 and is restrained from axial movement by retaining ring '76'. Stud 7S issecuredto the support housingod in any suitable manner. Gear 74 meshes` with gear 77 which is rotatably mounted on shaft 7S. A ve locity scale 79 is affixed to gear 77 and, by means of studs 79, to potentiometer housing 7h which carries resistance t) in a manner welfl known in the art. It now will be appreciated that rotation of knob 72 results in a rotation of potentiometer housing '71 with an indication of the magnitude of rotation givenrbyvelocity scale 70 and an indicator mark (not show-n) attached to the support housing 64.

It can be seen from the schematic diagram of Figure 2 that the potentiometer wiper 8l is connected through switch blade 82 of switch 83 to contact 54 ofswitch Si. Potentiometer wiper 8l is positioned in sliding contact with the logarithmetic resistance element 86 which is connected to a source of potential S4. Thus, when switch l is in the Manual position, i.e., with switch blade 52 connected to contact 54 and switch blade 5'5 connected to contact S7, a potential ER derived from the potentiometer 5S and the source of potential 84 is supplied to the central computer 1S. Conversely, when switch 5l is in the Scanner position, i.e., with switch blade 52 connected to contact 53 and switch blade 55 connected to contact 56', the ER potential is supplied by the optical scanner ltl and the scanner converter 11. Accordingly, it will be appreciated that switch 51 enables the operator to select the source of ER voltage from either the automatic scanner system .or the potentiometer means of the manual Computer.

It is manifest that the-ratio of V/ HA decreases with increasing altitude with a resulting decrease in the ER voltage. As the ER voltage decreases, the control voltages supplied to the servomotor 24 also decrease with the result that any errors increase proportionally in magnitude. In accordance with an aspect of this invention, this undesirable result is avoided by an automatic switching circuit in both the scanner converter 11 and the manual computer l2 whereby the ER voltage is increased by a factor of Whenever it falls below a rst predetermined level. Control signals thus raised by a factor of l() are termed High Altitude" signals. Similarly, the ER voltage is decreased by the factor of lO whenever the control signal returns to a second predetermined level. Advantageously two separate levels are provided for control of the automatic switching circuit. A single predetermined level could be used for this purpose, but this is not preferred due to the possibility of repeated switch-ing taking place for aircraft operation at or near this single level. This possibility is obviated by the provision of separated first and second predetermined levels. As the rER voltage supplied to the ampliier 25 in the central computer V14V controls the speed of the servo motor 24, the speed of the latter is increased or decreased by the Vfactor of 1,0 with this change in voltage.

Additionally, a reduction gear train in the `range gear changing mechanism lo is actuated by remotely controlled means whenever the High Altitude signal is present. This gear reduction is engaged to reduce output rotational speed by the same factor of 10 for High Altitude signals and is disengaged whenever the control signals are not in the High Altitude range. Thus, changes in the speed of servo motor A2d due to switching to a higher or lower voltage range are cancelled out and ythe servo `ference voltage is applied to amplifier 25,.

l@ system is operated within a speed range where inaccuracies are held to a minimum.A K

One illustrative means for accomplishing switching between High Altitude andnormal ER ranges is in the manual computer as shown in Figures 2 and 3. The potentiometer SS of the manual computer l2 has two wipers 8l and S75' placed with respect to each other such that the potential measured across wiper S5 and poten-v t-ial source 84 is l@ times the potential measured across Wiper 81 and potential source 84. A cam 86 secured to shaft 78 of the potentiometer changes the position of switch blades 82 and 87 of switch S3 in response to changes of the altitude setting. Thus, at the predetermined altitude level, the position ofswitch S3 changes and contact for switch blade 82 is transferred from wiper 8l to wiper 8S or from wiper 85 to wiper 8l. At the same time, switch blade 37 ofA switch 33 opens or closes a circuit between a source of potential d8 and contact 57 of the Scanner-Manual switch 5l for use when switch 51 is in the Manual position to supply power to a magnetic actuating means in the range gear changing mechanism lo. Thus, for the condition where l0` ER is supplied to the amplier 25, the gear reduction in range gear changing mechanism 16 is engaged, while for normal values of ER the gear reduction is disengaged It will be appreciated by those skilled in the art that the mechanical switch means for increasing the ER signal lO-fold as described above may be replaced by any other suitable electrical or electronic means capable of attaining the same result and in another illustrative embodiment it is contemplated that conventional voltage sensitive relays may be substituted for the switch 83 in the manual computer.

In accordance with a major feature of the invention, the ER signal data is converted to a shaft rotation having a velocity proportional to the amplitude of the ER signal by the velocity servo system of the central computer indicated generally at l5 in Figures l and 2. This servo system comprises a conventional arrangement of an amplier 25 connected at its output to a D.C. servo motor 24 and at its input to a D.C. generator 23. Motor 2,71 and generator 23 share a common armature shaft which also is coupled to the range gear changer lo.

The positive ER control signal from switch blade S2 of the Scanner-Manual switch 51 is connected to the positive terminal of D.C. generator 23 and the negative terminal of the generator`23 is connected to the input of amplier 25. ln this manner the diierence between the ER signal and the output voltage or" generator 23 forms the input to the amplifier 25.

When servo motor 24 is operating at a speed less than that required by the ER signal, the output voltage of generator 23 is less than the ER signal and a positive difference voltage is Supplied to the amplifier 25. Amplifier 25 has a current output which is proportional to the difference voltage applied to its input and for positive difference voltages the current output increases with increases in the voltage input.

The current output of amplifier 25 is applied to the armature of servo motor 24 and as the current output increases, the motor speed and hence the generator speed tends to increase. As generator speed increases the generator voltage increases to thereby reduce the difference voltage between the generator output and the ER command signal. This process continues until the difference voltage is reduced to zero at which time motor 24 is operating at the speed required by the ER signal.

It will be understood by those skilled in the art that when the servo motor 24 is operating at a higher speed than that required by the ER signal, the output of generator 23 is greater than the ER signal and a negative dif- Amplifler f2.5 then decreases its current output to the armature of servo 11 motor 24 and the motor is slowed down until it is operating at the speed required by the ER signal.

Accordingly, in the manner explained above, the output shaft of servo motor 24 is caused to rotate at a speed proportional to the V/H ratio, as controlled by the ER signal. Consideration of the operating characteristics of the servo motor 24 and of the gear ratios necessary in the station computers 29 indicates that it is desirable to maintain this proportion at ratios other than 1:1. A preferred ratio and one actually used in an embodiment of this invention sets the servo motor output speed at either 5.63 V/H revolutions per second or 56.3 V/H revolutions per second. As will become apparent from the description given hereinbelow, the output speed of the central computer line shaft 17, to which the station computers 29 are coupled, is maintained at a constant value of 5.63 V/H revolutions per second.

The coupling of the output shaft 91 of servo motor 24 to the range gear changing mechanism 16 is shown in greater detail in Figures 4, 5, 6, 7 and 8 of the drawing. The range gear changing mechanism is a form of transmission with a preferred velocity ratio from input to output of either 1:1 or 1:10, as desired. Manifestly, other ratios may be employed in lieu of these preferred ratios with equally advantageous results.

As shown in Figure 4 the output shaft 91 of servo motor 24 is rotatably mounted in bearings 92 and 93 which, in turn, are secured in any suitable manner to the supporting structure 94. Gears 95 and 96 are secured to shaft 91, as for example, by threaded split hubs (not shown) attached to thegears together with nuts 97. Advantageously, retaining rings 98 may be positioned in annular grooves provided in shaft 91 to maintain the shaft, and hence gears 95 and 96, in a desired axial position.

The output shaft 17, which is the central computer line shaft, of the range gear changing mechanism 16 is rotatably mounted in bearings 99 and 100 which, in turn, are secured to the supporting structure 101. Retaining rings 102 are positioned in annular grooves in shaft 17 to maintain the shaft, and hence gears 103 and 104, in position axially. Gear 104 is rotatably mounted on line shaft 17 so as to mesh with gear 96. Gear 104 is restrained from axial movement by retaining rings 105 set in annular grooves in line shaft 17. Gear 103 also is rotatably mounted on line shaft 17 and is in mesh with gear 95. Gear 82 is restrained for axial movement by retaining rings 106 set in annular grooves of line shaft 17.

In the illustrated embodiment, gears 96 and 104 are identical and hence have a velocity ratio of 1:1. Gear 95 advantageously is smaller than gear 103 and in this ernbodirnent the gears have a velocity ratio of 1:10. In accordance with an aspect of this invention, either gear 104 or gear 103 may be operatively coupled to line shaft 17 for rotating the latter by the gear shifter coupling generally indicated at 107 in Figure 4 and illustrated in greater detail in Figures 5, 6, 7 and 8.

In Figure 5, the gear shifter coupling 107 is shown in the position for providing a 1:1 velocity ratio transmission from input shaft 91 to output line shaft 17. The coupling has a body 108, which advantageously may be an integral enlarged diameter of line shaft 17. The body 108 is provided with an annular groove 109 and a radial hole 110 to provide clearance for a spring 111. This is shown in greater detail in Figure 8 where it can be seen that the shape of spring 111 is such as to maintain the spring in position in groove 109 once it is pressed into this position. A formed central portion 112 of spring 111 tends to keep the spring in the position shown in Figure 5. A notch 113 at one edge of central portion 112 of the spring 111 operatively engages an annular groove 114 in driving pin 115. Driving pin 115 is assemberl through two aligned holes in body 108 in such a manner that it has rotational freedom and is limited in axial movement by the central portion 112 of spring 111.

A selector pin 116 is positioned in an axial clearance hole in line shaft 17 and advantageously is made of sufcient length to contact the central portion 112 of spring 111 at one end of the pin and to extend beyond the end of line shaft 17 at the other end of the pin. It can be seen that if selector pin 116 is moved to the right from the position shown in Figure 5 it would overcome the spring force exerted by the central portion 112 of spring 111 and cause the central portion of the spring to assume the position illustrated in Figure 6. It will be noted that as the spring central portion 112 is moved to the right, it causes the driving pin 115 to move to the right along with it.

One preferred method for actuating the selector pin 116 is by the energization of the solenoid 117 shown in Figure 4. When the Solenoid is energized, its armature 118 is placed into contact with selector pin 116 to move the selector pin to the right from the position shown in Figure 4 of the drawing. It now is understood that this results in driving pin 115 also being moved to the right with respect to its illustrated position in Figure 4.

When the solenoid 117 is de-energized, the coupling is in the normal position illustrated in Figure 4. In this position driving pin 115 is held by the pressure of the spring central portion 112 in a position where it will intercept longitudinally a pin 119 secured to gear 104 upon rotation of this gear. When the input shaft 91 is rotated by servo motor 24, gear 96 and its meshing gear 104 also are rotated. This causes pin 119 on gear 104 to engage driving pin 115 and the resulting rotary force is transferred to coupling body 103 to rotate line shaft 17 at a speed identical to that of shaft 91. It will be appreciated that as the servo motor driving shaft 91 is constrained by its method of connection to a single direction of rotation, back lash is of no consequence.

When the solenoid 117 is energized by the High Altitude signal over conductor 27 from the manual computer 12 or the scanner converter 11, as described above, selector pin 116 and hence driving pin 115 are moved to the position shown in Figure 6. In this position, driving pin 115 does not intercept pin 119 on gear 104 but the driving pin does intercept pin 120 secured to gear 103. When the servo motor output shaft 91 and gears 95 and 103 are rotated, pin 120 on gear 103 intercepts driving pin 115 on the coupling 107. Consequently, coupling 107 and hence line shaft 17 are rotated at a speed 1/10 of that of shaft 91 because of the reduction interposed by gears 95 and 103.

Referring now to Figure l of the drawing, it can be seen that line shaft 17 extends a considerable distance from the range gear change mechanism 16 to drive several additional components. Additionally, it now is understood that line shaft 17 is rotated at a speed proportional to the V/H ratio in accordance with signals supplied by either the optical scanner 10 or the manual computer 12. As shown in Figures l and 2, a synchro transmitter 18 of conventional design is coupled to the line shaft 17 such as by gear 121 secured to the line shaft and its meshing gear 122 coupled to synchro transmitter 18. As explained in greater detail below, synchro transmitter 18 is utilized to supply to the system a rotational data reference potential which is a function of the V/H information.

A plurality of station computers 29, such as those shown at computer station units 19, 20, 21 and 22, are detachably coupled to line shaft 17 at spaced intervals along the length of the line shaft. As shown in Figure 2, each station computer 29 is preferably coupled to line shaft 17 by means of a pair of miter gears 123 and 124; gear 123 is secured to line shaft 17 and gear 124 is se cured to stub shaft 125. Advantageously, each station computer 29 is detachably coupled to its stub shaft 125 by means of a male coupling 126 secured to the stub shaft which is adapted to engage a female coupling 127 secured to the input shaft 128 of the station computer 29.

13 The male coupling 126 and the female coupling 127 are keyed to lit together in only a single predetermined fashion for 360 of rotation to the end that the phase relation therebetween be constant, as explained further below.

The principal features of the construction of a station computer 29 are shown in Figure 9 of the drawing. Input rotational motion to the station computer 29 is effected by female coupling 127 secured to one end of the station computer input shaft 128. Shaft 128 is rotatably journaled in a bearing 129 and carries at its other end miter gear 130. Miter gear 130 is in mesh with miter gear 131 which is secured to the station computer drive shaft 132. Shaft 132 has affixed thereon a gear 133 in meshY with gear 135 and a gear 134 in mesh with gear 136, each of the gears 135 and 136 being carried by shaft 137.

A plurality of other shafts and gears are provided in station computer 129 and like shafts 132 and 137; each of these shafts is rotatably mounted in suitable bearings provided in frames 138 and 139.

Table I below describes the relation of the various gears and various shafts in the station computers and preferable gear ratios which obtain between various numbers of the gears:

TABLE I Mesh es with- Prr fe rrr d Shaft No. Gears naar Ratio Gear On Shaft 134 136 137 22 132 i 133 135 137 1 1,56 134 132 22 137 135 133 132 1 1-10 143 14 2 1 141 144 142 5 143 140 137 144 141 137 142 146 14s 149 5 145 147 149 1 148 146 142 5 149 147 145 142 1 150 152 154 75 151 153 154 1 152 150 149 75 154 153 151 149 1 156 158- 1 9 1 155 157 159 93 158 156 154 1 159 157 155 1F4 .93 Y

Advantageously, each of the shafts 137, 142, 149, 154, 159 and 160 is provided with a gear shifter coupling 107 of the type shown in Figures 4, 5, 6, 7 and 8 between a 7 pair of gears carried by the shaft. These gears, i.e., the gears having gear shifter coupling 107 positioned therebetween are rotatably mounted with respect to their shafts. The remaining gears are each xedly secured to the shaft so as to rotate therewith. Further, it will be understood that each shaft having a gear shifter coupling thereon is hollow to provide clearance for the coupling selector pin 116, as described above.

Advantageously, a manually operated push button or remotely controlled operating means such as a solenoid, or both, is associated with the selector pins of each of the gear shifter couplings 107. Where only a solenoid is provided to effect the gear changing through a gear shifter coupling, a solenoid such as that schematically indicated at 175 in Figure 9 may be secured to a supporting structure by suitable fastening means (not shown) so that the solenoid plunger 176 is aligned with the selector pin 182 of coupling 167 on shaft 137. Thus, when solenoid 175 is energized its plunger 176 is actuated to move selector pin 182 to the right from the position shown in Figure 9 14 to effect a change in the position of the driving pin of the gear shifter and hence to change the operating gear ratio between shaft 132 and 137.V

Still another preferred embodiment of a switching solenoid to effect gear changing is shown in Figure 9 by the solenoid indicated `at 177. When the solenoid 177 is energized its plunger 178 contacts bell crank 179 which is pivotally mounted on pin 189. The bell crank 179 pivots counterclockwise on pin 180 to depress selector pin 181 on shaft 142. One advantageous feature of this arrangement is that a push button, such asV that indicated at B, also may be used to pivot the bell crank 179.

It will be understood that each of the gear Shifters in the station computer may be operated by either a solenoid of the types described above or a push button, such as those indicated at A, B, C, D, E and F for shafts 137, 142, 149, 154, 159, and 160, respectively, or by both a solenoid and a push button, if desired.

1t is contemplated that the push buttons and the solenoids are of the type which remain in their actuated positions until they are released. Suitable push buttons and solenoids adopted for this purpose are known to those skilled in the art.

Now it can be appreciated that in accordance with the novel features of this invention, operator set up of the various gear ratios necessary for integration of the preflight variables into the station computer computction can easily and quickly be effected by means of the button and/ or solenoid associated with each of the gear shifter couplings. The cooperation between the shifter couplings, the selector pins and the push buttons, together with the gear ratios obtained for each sele'tor pin in its opelrated or released condition, are given in the following tab e. i

TABLE II Associated Preferred Gear Ratio Shifter and Button Designation Shaft Selector Shifter Shifter Pin Depressed Released 1t will be appreciated that the total station computer gear ratio for the illustrative station computer embodiment shown in Figure 9 is the product of the six individual gear shifter ratios. Further, it will be appreciated that the over-all gear ratio of the station computer may be varied as desired to obtain various picture taking rates. To determine the gear ratio, GR required for a specied picture taking rate, R, in pictures per second, the following equation may be used:

RH GR-assv (3) where the variables H and V have the same meanings described hereinabove.

A preferred method that may be used to obtain the station computer gear ratio, where the overlap and the other pre-flight variables have been specified, is by the use of a chart wherein the gear ratios for the more commonly used values of pre-flight variables have been pre-computed. This serves to substantially simplify the operators task, for all he need do is refer to the chart and depress the combination of push buttons indicated thereon. For eX- ample, the embodiment of station computer illustrated in Figure 9 of the drawings advantageously may have associated therewith an' instruction plate containing the information tabulated in Table III below for indicating the proper combinations of push buttons A, B, C, D, E and F to be depressed for predetermined sets of pre-Hight variables:

16 computer with sixV gear shifter couplings and the various gear ratios indicated in Table II are merely illustrative ofthe invention.

Referring now to Figure 10, there are Yshown two pulse TABLE III Focal Length Format-@gm Direction: 6 12 Optical Axis Overlap,

Percent Push In Buttons Depression Angle 90 None B BCD BC BDF F 90 BE BCE BDEF BEF BCDEF BCEF 15 B BC BDF BF BCDF CF BD BCD BC BDF BF BCDF 15 None C DF CDE` CF ACD DE None BDE B BCDE 5 DE BDE BCDE BC BDEF Referring again to Figure 9, it can be seen that the synchro transmitter advantageously may have its rotor driven at the same speed as the output of the station computer. The phase relationship of the synchro transmitter output is established with respect to a fixed position of the input coupling 127'and hence the line shaft 17 of the central computer. At this position the electrical zero ofthe synchro transmitter 30 is set. Positive location of the electrical zero of the synchro transmitter 30 with respect to the coupling 127 is made by the design of the gear shifter couplings 107 wherein driving contact between a gear and the couplings is eifected in only one position for each revolution of the gear. As a result, the electrical zero and the phase relationship of the synchrortransmitters in the diierent station computers can beV made substantially identical for a given line shaft angular position if the shifter settings in the dilerent station computers are the same.

The output of the synchro transmitter 30 thus provides a rotational IMC reference potential for one or more cooperatingv cameras at a given camera station. A cam 174 secured to shaft 173 is rotated at one half the speed of the station computer output by means of the reduction eiected by gear 171 on the synchro transmitter shaft 170 and gear 172 on shaft 173. A pair pulse switches 175 and 176 are operatively associated with cam 174 and are positioned with respect to cam 174 to be alternately closed thereby, i.e., one switch of the pair is closed for each 180 of cam rotation. Further, switches 175 and 176 are located with respect to a iixed position of the input coupling 127 in a manner similar to that described above for the synchro transmitters 30 to the end that like switches of different station computers are closed at substantially the identical instant in time if the. shifter settings in the different stations are the same.

It will be understood by those skilled in the art that more or less than two switches may be used with cam 174, provided the gear reduction between the switch operating cam shaft 173 and the station computer output is changed accordingly. It will further be understood that the number of couplings and the numerical value of their various corresponding gear ratios given in the above description of a station computer can be changed in accordance with the requirements placed on the control system, and that the foregoing description of a station cameras 177 and 178, which are connected for either simultaneous or alternate sequential operation. A station computer, generally indicated at 179, has a suitable gear reduction from its output driving shaft V173 with its attached cam 174 to alternately effect closure of the two switches generally indicated at and 181. A source of potential 182, which has its negative terminal connected to ground, has its positive terminal connected to the switch blades 183 and 184 of switches 180 and 181, respectively. The stationary contact 185 of switch 181 is connected to pulse camera 178 and the stationary contact 186 of switch 180 is connected to pulse camera 177. In actual practice, suitable pulse shaping circuits having a pulse output of constant duration regardless of pulse separation would be provided between the switches and the pulse cameras, but for the purpose of simplifying the explanation of the switch operation, these Ypulse shaping circuits have not been shown.

It now can be seen that with no connection between the conductors leading7 to pulse cameras 177 and 178, a pulse resulting from the closure of switch 181 actuates pulse camera 178 and similarly, after 180 of rotation of cam 174, a pulse resulting from the closure of switch 180 actuates pulse camera 177. It can readily be seen that if the conductors to the two pulse cameras are connected together, as by a conductor 187 shown dotted in Figure 10, closure of either switch 180 or 181 will actuate both cameras. Further, if only one camera is used, the inclusion of conductor 187 would result in that camera receiving pulses at the computed rate. Manifestly, inclusion of the Vconnecting conductor 187 can be made either permanently orY by a relay operated from some remote location.

Figure 11 is a 'simplified schematic diagram which shows in greater detail than in Figure l the connection of an autocycle camera 36 to the control system of the invention. The gear train of the station computer 29 drives the rotor 188 of synchro transmitter 30 at a speed proportional to the camera cycling rate. Rotor 188 receives power from a transformer 189 in the servo arnplifier 37 by means of conductor 217. As the rotor 188 is rotated, varying voltages are impressed on the several stator windings 190 in a manner well known in the art.

A synchro receiver 191 located in the autocycle camera 36 has itsstator windings 192 connected to the stator 'windingsj190 of the synchro/transmitter 30 'in the station tate'the following explanation of the operation of theV autocycle camera, rotor winding 197 will be designated as'camera B winding and rotor winding `196 will be designated as camera A winding. The camera B winding 197 is in phase with the rotor 188 of the synchro transmitter 30 when the camera drive motor is rotating at the correct speed, and for zero phase relation the outputlfrom the camera B winding 197 will be at a maximum. The output of the camera A rotor winding 196 vwill be low under these conditions. Since the film drive mechanism 198 is driven by the film drive'motor 19,4 simultaneously with therotor 193 of the synchro receiver 191, for an in -phase relationship between the rotors of the synchro transmitter 30 and the synchro receiver 191, the film will be moved at the IMC velocity.

Here another of the features of this vinvention becomes apparent. The two synchros in combination with the film drive motor 194 and the servo amplifier 37 comprise a positional servo mechanism utilized as a Velocity control device. The importance of this feature is evident when it is recalled that although a positional servo mechanism is subject to certain positional errors with respect to the synchro transmitter, its velocity error is substantially zero.

Since the power supplied to the rotor 188 of the synchro transmitter 30 by transformer 189 advantageously isderived from the aircraft power system, the frequency of its output will be 'that of the aircraft power system, a frequency which commonly is 400 cycles per second. As a result, the output of the camera ysynchro rotor 193is a 400 cycle signal which is modulated at a frequency dependent on the speed difference between the two synchros. For example, if the relative motion between the two synchros is 60 r.p.m., then the modulation frequency is 1 cycle per second.

An illustrative example of the waveform of the camera synchro output when a speed difference exists is shown in Figure 12. When the camera is running at synchronous speed, but out of phase, the output is that of the waveform shown in Figure 13. It will be noted from Figure 13 that both output conductors from the synchro receiverV rotor windings 196 and 197 have a signal amplitude proportional to the 400 cycle supply frequency, but no modulating frequency.

The outputs of the camera A winding 196 and the camera B winding 197 of the synchro receiver rotor 193 are applied to separate demodulation circuits in the servo amplifier 37. Camera B winding output is applied to demodulator 199, and camera A winding output is applied to demodulator 200. The demodulator outputs are shown in Figure 14 of the drawings. Direction arrow 201 in Figure -14 indicates wave progression for increasing time whenthe receiver synchro rotor 193 is underspeed and where signalA leads signal B. Direction arrow 202 in Figure 14 indicates wave progression for increasing time for the overspeed case where signal B leads signal A. It will be understood by those skilled in the art that phase reversal occurs whenever a camera synchro operating underspeed begins to operate overspeed or vice versa.

The outputs of demodulators 199 and 200 are applied to a logical computer 203 which serves Ato detect if camera A signal or camera B signal is'leading. In addition, the camera A conductor from demodulator 200 applies an'error. signal to a voltage amplifier 204 which controls the output of a magnetic amplifier 205. v Al-` though amplifiers 204 and 205 may be constructed in accordance with voltage and magnetic amplifiers well known to those versed in `the electronic arts, an illustrativeconstruction Jfor these amplifiers is :shown in the.

1 mitter synchro 30 andthe camera drive motor, the

logical computer 203 functions. For overspeed, the power I Supply fraai losisal @imputer 2,03 t9 the magneti@ amati,- fier 20S by way'of conductor 206 is opened'For underspeed, a very large (in comparison to the A error signal) error signal is added from logical computer 203 to thel output of amplifier 204 by way-of conductor 207. This signal, occasionally referred to as a slugging signal, results in a relatively large output fromamplier 202i and causes maximum power output of magnetic amplifier 205. When the motor 194 and synchro receiver .193 areft the command speed, the computer 203 maintains power? to the magnetic amplifier, but does not Vslug amplifier 204. In this case, only the A error signal is present at the input of amplifier'204gfand it controls the two amplifiers to cor-` rect for any small difference in phase angle existing be-v tween the'two synchro rotors 190 and 193.

An illustrative embodiment of servo amplifier 37 is shown in schematic form in Figure l5 of the drawings. When the system master on-o switch and the station H power are on, D.C. power is supplied to the servo amplifier over conductor 210 and 400 cycle A.C. power is supplied to the servo amplifier over conductors 211'and'212. Conductor 212 is connected to primary Vwinding 213 and the A.C. voltage thereon energizes transformer 189. Secondary Winding 215 oftransformer 189 supplies heater power to the various electron tubes. Winding 216 suppliesMexcitation 15S/conductor 217`t'o 'the 'rotor 188" of the synchro-transmitter 19`0in the station computer. Winding 214 supplies the AlCjvoltageinput for full wave rectifier 218 which comprises a bridge arrangement of diodes 219,220,221 andA 222.n Rectifier 218 is connectedtits output to a filter comprising choke -244 and capacitor 245i and serves as the D.C. voltage supply over conductor 268f for the anodes of electron tubes 224, 225 and .226 in vservol amplifier 37 The modulated signals from camera A winding1196 and camera B Winding 197 of synchro receiver rotor 193` are applied to separate windings 227 and 228, respectively, on transformer 189. The camera B signals are d emodulated in the circuit consisting of resistor 229;, diodes 230 and 231, resistor 232 and capacitor 233. The cameral A signals are demodulated inthe circuit consistingof resistor 234, diodes 235 and 236, resistor 237 and capacitorv 238. Advantageously, the resistors in each demodulatc'nV circuit are maintained substantially equal so that the voltage amplitude at the input will equal the voltage amplitude at the output. y

The demodulated camera B output-from demodulator 199 is applied to the grid 240 of tube 224A 'through bias resistor 239.' The demodulated 'camera A output" from demodulator 200 is applied to the grid 243 of tube 224B through bias resistor 241, and through biasl resistor 242 Vto the input of a conventional voltage amplifier generally indicated at 204 and comprising tubes 225 and 226.- The anode current of tube 224A controls the coil modulated signall is leading and:hencewhether'thef camera is operating overspeed or underspeed.

Tables lV and V, which summarize the relay conditions for thevarious phase angles of demodulator output,V

are set out below to facilitate the ldescription of computer operation. Table IV corresponds tothe direction` arrow V201.irrth'e phase diagram of Figurel4`, `and.Tablefr V @Qlresponds to the direction arrow3202.A

TABLE IV v Underspeed Relay 6 Slgnal Sllial Ampller-204 Rl R2 R3 R4 O-E- N E N Proportional 2 Control.

ri; E E n E slugging.

-32" 2f N E E E no.

air-? N N E E Do.

r--31r E N E N Proportional 2 Control.

arl; n E E E slugging.

-2-41 N E E E D0.

4f-92l N N E n Do.

N= Not energized, E=energlzed.

TABLE V Overspeed Relay 0 SlgAnal Slgial Amplifier-204 R1 R2 R3 R4 ggf-4f N N E E slugging.

41r-2 -1- N E E E D0.

72f-af E E E E D0.

31: E N E N Proportional 2 Control. 51|' -2-1- -l- -I- E E N N D0.

J E N N N Do.

,-0 N E N Proportional 2 Control.

N Not energized, E=energized.

When the camera is operating underspeed and the station operate switch 250 is closed, the following conditions obtain. Closing of the operate switch 250 completes a circuit from ground through diode 251, resistor 252, coil 253 of relay R3, normally closed contacts 254 of relay R2, normally closed contacts 255 of relay R1 and conductor 210 to D.C. voltage source 256. Operate switch 250 also completes a circuit from ground through diode 257 and resistor 258 to the cathodes 259 and 260 of tube 224. Assuming for convenience that the operate switch is closed at t=0 in Figure 14, the following occurs during the irst quarter cycle, or from phase angle zero to zr/ 2.

During this period, both of the camera A and camera B error signals are negative so that neither half of tube 224 conducts and relays R1 and R2 are not energized. D.C. voltage from source 256 is applied over conductor 210 through the normally closed contacts 255 of relay Rl, and the normally closed contacts 254 of relay R2 to coil 253 of relay R3 which is then energized. Relay R3 when energized closes its normally open contacts 261, 262, and 263, respectively. This establishes a new D.C. voltage path to maintain coil 253 of relay R3 energized through its contacts`262. Also, contacts 263 of relay R3 areA closed to apply 400 cycles A C. voltage from conductor 211 to the magnetic amplifier 205.

During this period, with the camera A error signal negative, the output of amplifier 204 signals the control windings of magnetic amplifier 205 to decrease the speed of the camera servo motor 194 in a manner analogous to, but the reverse of, that described below for the next quarter cycle. Current ilo-w through the magnetic amplitier 205 is reduced to that required for magnetizing and, since this is far less than that required by the motor 194 to start, it remains stopped. l

During the second quarter cycle or from 1r/ 2 to 1r, the camera A signal is positive and the camera B signal negative. Tube 224B then conducts to energize coil 248 of relay R1. Relay R1 operates to open its normally closed contacts 255 and to close its normally open contacts 264. This transfers the D.C. voltage from source 256 from contacts 255 to 264 of relay R1 from whence it is applied through the normally closed contacts 265 of relay R2 and through resistor 266 to ground. Relay R3, and hence magnetic amplifier 205, remain energized since relay R3 continues to be supplied through its now closed contacts 262. Since the camera A signal is positive,v

tube 225A of ampliiier 204 conducts and drives the grid of tube 226B more negative. When the grid of tubo 226B goes negative, tube 226B is cut ofi, and with it the control winding 267 of magnetic amplifier 205 that is connected between the tube D.C. voltage supply conductor 268 and the anode of tube 226B.

As the grid of tube 225A goes positive with the A error signal, its cathode 269 and cathode 270 of tube 225B tend to follow. This develops a positive going potential at the anode of tube 225B and, hence, at the grid of tube 226A. Tube 226A conducts and current ows from ground through resistance 268, tube 226A and the control winding 269 of the magnetic amplier 205, to the D.C. voltage supply conductor 268. This current flow increases the saturation of the core of the magnetic amplifier 205 and current flows to the full wave bridge rectifier 284 comprising diodes 271, 272, 273 and 274, respectively, which supplies the film drive motor 194 in the camera 36 through conductors 275 and 276. Motor 194 starts, and its speed increases in pro portion to the magnitude of the camera A error signal.

Assuming that camera 36 does not reach the command speed for some time and phase reversal of the A and B signals does not take place, then in the third quarter cycle from 1r to both the'camera A and camera B signals are positive. As a result, both halves of tube 224 conduct to maintain the coil 248 of relay R1 energized and, further, to energize the coil 247 of relay R2. Relay R2 operates to close its normally open contacts 277 and 278. This completes a D.C. voltage circuit through the now closed contacts 264 of relay R1,'the now closed contacts 278 of relay R2, the now closed contacts 261 `of relay R3, coil 279 of relay R4, and resistor 266 to ground.

Thus energized, relay R4 operates to close its normally open contacts 280 and 281. Closure of contacts 281 establishes a new D.C. voltage circuit to maintain coil 279 of relay R4 energized. Also, the closure of contacts 280 of relay R4 applies the D C. voltage on conductor 210 to the input of amplifier 204, i.e., at the grid of tube 225A, through now closed contacts 262 of relay R3, coil 253 of relay R3, now closed contacts 280 of relay R4 and bias resistor 282. This potential is very large in comparison to any camera A signal and..

2221 hence it f is -termed a .slugging potential. .:It is present whenever relay R4 is energized. Amplifier '204 `responds byapplying a large potential dierence to the control windings 267 and 269 of magnetic amplifier 205. This saturates the magnetic amplifier 205 and maximum current then fiows to the camera drive motor 194 through magnetic amplifier winding 283, full wave Abridge rectifier 284 andconductors 275 and 276.

During the fourth quarter cycle from relay R1 is de-energized in-the manner described heretofore-since the camera A signalisnegative. The camera B .signal remains positive and consequently. relay R2 remains energized. The D.C. voltage circuit through Acontacts 255 of vrelay R1 andcontacts 277 of relay vR2 is opened at icontacts 285 lof relay R4. Relays R3 and R4 remain energized so thatnotonly the'applied power but also slugging of amplifier 204 and magnetic amplifier 205 continues.

From

in the fifth quarter cycle, both relays R1 and R2 are 'deenergized since both the camera A and B signals are negative. Relays R3 and R4 remainenergized and full power continues to be applied to the film drive motorr194.

In the sixth quarter cycle from the 'camera A signal is positive and the camera B signal is negative. Thus, relays R1,R2 and R3 are in the same condition as in the second quarter cycle from 1r/2 to 1r described above. The D.C. voltage applied to the ground side of coil 279 of relay R4 through now closed contacts 264 of relay R1 and normally closed contacts 265 of relay R2 causes relay R4 to become de-energized. This opens its contacts 280 to stop the slugging of amplitier 204, and proportional control of film drive motor speed 194 by the camera A signal resumes.

In the event that the lm drive motor 194is not yet up to command speed, the following four quarter cycles are the same as those in the period from 1r to 311-, etc. As soon as the camera motor 194 operates overspeed,-a phase reversal of the demodulated camera error signals takes place and camera B signalleads camera A signal. vAssuming'that the motor goes overspeed while receiving a slugging voltage to increase its speed and that phase reversal of the A and B signals occur at 91r/2 in Figure 14, the chart of Table V, supra, applies together with direction arrow 202 of Figure 14.

In the first quarter cycle of Figure 14 from to 41r in the overspeed direction, both camera A and camera B signals are negative. Hence, relays'Rl and R2 are deenergized. Relays R3 and R4 remain energized and "full power continues to be applied to the film drive motor 194 to increase its speed.

In the second quarter cycle of overspeed, from 4nto the camera A signal is negative and the camera B signal positive. Therefore, coil 247 of relay R2 is energized and relay'Rl remains de-energized. The D C. voltage circuit through relay contacts 255of relay R1 and con- .tacts 277 of relay R2 is opened at contacts 285 of relay `R4. Relays R3 and R4 remain energized andfull power continues to be applied to the camera film drive'motor '194.

inLthe third quarter cycle,'both cameraA andcameratB signals are positive, and'all'four relaysR1,R2,;R3:and R4 are energized. Consequently, full power to the motor 194 continues.

In the fourth quarter Vcycle of overspeed from 31r to the camera A signal'ispositiv'e and-the lcamera B-'fsgnal isY negative, thereby de-energizing relay R2. TheiD'C. voltage on conductor -210 thenis applied through-icon# tacts -264 of relay R1 and contacts-265 of rely-R2t`o theground side of coil-279` ofrelayl R4,-thereb'y de=en`efr gizing relay R4. This opens contacts 280 .ofrela'y'lR4 to stop the slugging of amplifier 4204. Since relay R3 remains closed and the camera A ysignal is positive, power to the camera film drive motor 194 continues andthe motor continues to increase in speed.

`It should be notedthat theY example illustratedin Figure 14 is for the worst possible conditions, i.e., -where the motor reaches overspeed and-phase reversal occurs at or slightly prior to Under these conditions, the motor '194 continueswtfin crease in speed for four one-quarter cycles of the modulating frequency. While this is not probable'in actual operation, if it does occur, then both the modulating frequency and the camera A errorsignal increase as the motor increases the error between its speed and the command speed. VHence, the time perio'd consumedin these four quarter cycles'sis relatively short, and `as' the camera A error signal is comparativelyelarge, the motor will assume the command speed quickly.

From

5 2."- to 2'1r in the fifth quarter cycle, both camera A and camera"B signals are negative. Relay R3 remains energizedand relays R1, R2 and R4 de-energized. Since the camera'A signal is negative, amplifier'204 reverses the current to the control windings 267 Aand 269 of magnetic amplifier 205. This decreases the current ow through the magnetic amplifier and the film drive motor'194`is slowed down.

In the sixth quarter cycle from the camera A signal is negative and the cameraB signal is positive. Relays R1 and R4 remain de-energized,` and relay R2 is energized. This establishes a D.C. voltage circuit through contacts 255 of relay R1, contacts 277 of relay R2, and contacts 285 of relay R4 to the ground side of coil 253 of relay R3. This de-energizes R3 and opens its contacts 263 which supply A.C. voltage to winding 283 of magnetic amplifier 205. With the magnetic amplifier 205 cut off, all power tothe camera film drive motor 194 is cut off and its speed decreases.

Assuming that camera sped continues to be greater than the command `speed so that phase reversal of the error signals does not occur, `the magnetic amp1ifer.205 andthe motor 194 will remain cut oi untilboth'ofthe camera A-and B signals are negative as in the period from to 21r. In this 'quarter'cycle,'relay R3 is energized and 23 with it the magnetic amplifier 205 as described hereinabove. Motor speed will continue to decrease during this period since the camera A error signal is negative, but if phase reversal does take place, proportional control by the camera A error signal continues in the next quarter cycle, as for example, the period from of Figure 14, and the motor 194 will increase in speed since camera A signal will be positive.

When the station computer synchro 30 and the camera synchro 191 are running at the same speed, there is no modulating frequency output from the rotor 193 of the camera synchro. As described hereinabove, for a zero phase angle and synchronous speed between the rotors of the two synchros, the output of the camera B winding 197 is at a maximum and the output of the camera A winding 196 is substantially zero. The output from the demodulators 199 and 200 of the servo amplifier 37 reilects this condition. The demodulated camera B signal is at a maximum and negative while the camera A signal is substantially zero.

For slight errors in phase angle, the demodulated camera B output is slightly less negative and the camera A slightly more or less than zero. If the rotor 193 of the camera synchro 191 leads the rotor 183 of the station computer synchro 30, the camera A demodulated error signal is negative and hence reduces the power to the camera film drive motor 194 tending to drop it into phase. If the rotor 193 of the camera synchro 191 lags behind the rotor 188 of the station computer synchro 30, the camera A demodulated error signal is positive and hence increases amplifier power to the camera film drive motor 194 to attempt to bring it into phase.

As described heretofore, autocycle cameras are capable of providing their own shutter tripping pulses and are further capable of controlling the overlap of successive pictures as a function of ca mera design. It will be appreciated by those skilled in the art that because shutter trip is not independent of IMC, it is more difficult to provide for alternate sequential exposures in autocycle cameras than with pulse or pulse IMC cameras.

It is contemplated, however, to provide sequential operation of two autocycle cameras with the control system of the invention. This is attained by altering the pattern of push buttons depressed on the station computer so that one-half of the desired picture taking rate is present at the station computer output. One autocycle camera and its associated servo amplifier then are controlled in the manner described above. The second autocycle camera has its stator input shifted electrically 180 and is controlled in a similar manner. Both autocycle cameras in a system of this type would have gear Shifting means adapted to double the speed of the film during the period that it is moving at IMC speed.

The IMC lm speed of continuous strip cameras advantageously can be controlled in the same manner as that described for autocycle cameras. However, a D.C. generator tachometer may be added to the shaft of the camera drive motor. The output of this generator tachometer then is used as a speed reference by an exposure control system to automatically vary the width of the camera slit as a function of film speed.

The system'connections for the simultaneous operation of two pulse IMC cameras 300 and 301 is shown in the simplified diagram of Figure 16 of the drawings. Camera 300 has operatively associated with it a servo amplifier 302 and camera 301 has operatively associated therewith a servo amplifier 303. Each camera and servo amplifier combination operates with respect to film IMC speed in the same manner as described heretofore for an autocycle camera. Unlike autocycle cameras, however, the pulse IMC camera does not originate itsv shutter 24 tripping pulse but rather it depends upon an outside source for such pulses.

In Figure 16, the IMC film speed of the two cameras 300 and 301 is controlled by the synchro transmitter 30 in station computer unit 20 and the shutter controlling pulses originate in station computer unit 19 at the switches 304 and 305 therein. It will be understood that by thus separating the command sources for IMC film speed and shutter trip of -a pulse IMC camera, it is possible to vary the overlap of successive photographs.

When the operate switch 306 is closed, a connection is provided between ground and the switch blades of the two pulse switches l304 and 305. Also, a ground connection is provided for the camera servo amplifiers 302 and 303. The film in each camera is moved at IMC speed until one of the two pulse switches 304 and 305 is closed by the action of cam 174. This operates the shutters of both cameras which then signal their respective film drive mechanisms to advance, at high speed, a fresh supply of film to the exposure area. After the film is advanced, the IMC speed is resumed until the next shutter operation.

A pulse IMC camera connected for day or night operation is shown diagrammatically in Figure 17 of the drawings. Camera 307 and its associated servo amplifier 308 are operated vin an identical manner in either the day or night mode with respect to the film IMCl speed under the control of the synchro transmitter 30 in the station computer. This operation is the same as that described above for `autocycle cameras. With switch 309 in the flare release panel 310 open, as shown in Figure 17, the system is set for day operation.

Cameras used for both day and night operations usually have two electrically operated shutters arranged out of phase with respect to each other. That is, when one shutter is open the other is closed and as each pulse is applied to both shutters these conditions are reversed.

In day operation, the shutter pulses originate at either of the switches 304 and 305 in station computer unit 19 and the pulses are fed through the normally closed contacts of switch 311 in station relay box 312 to a shutter control 313. The shutter control 313 is activated during day operation by closure of the operate switch 314 which connects shutter control 313 to ground through the normally closed contacts of switch 315 in the station relay box. The closure of either switch 304 or 305 by cam 174 results in the circuits of the shutter control 313 applying a pulse to the closed camera shutter to open the latter and, after a predetermined period of time, applying another pulse to the camera to close the second shutter and advance the film.

`Conversion of the system shown in Figure 17 to night operation is made by closing the ready switch 309 on the are release panel 310. This causes a potential to be supplied from source 316 to one terminal of the relay coil 317 and to the flash detector 318. Closure of the operate switch 314 connects the other terminal of relay coil 317 to ground and thus energizes the relay coil. Relay coil 317, when energized, controls the switch blades of switches 311 and 315 to enable pulses from the station computer to be transferred by switch 311 from the shutter control 313 to the flare ejector 319 through switch 309. The energizat-ion of coil 274 also de-energizes the shutter control 313 and energizes a camera circuit which opens the closed shutter and transfers the initiation of film re-cycle from the exposure control to the other camera shutter.

Pulses caused by the closure of either switch 304 or 305 result in a release of either a iash cartridge or a flare bomb, depending upon which is provided, from the flare ejector 319. When the flare or bomb explodes, the flash is detected by the flash detector 318 and the latter closes the open shutter of the camera and initiates re-cycle of the film. During this re-cycle, the shutter which was just opened is once again closed and the shutter which was 

